JPH09180717A - Nickel electrode for alkaline storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrict the lowering of the charging efficiency in the high temperature without lowering discharging electric potential so as to provide an electrode having the excellent charging and discharging efficiency by containing a rare earth element in the nickel hydroxide as a main component of the active material in the solid solution condition. SOLUTION: In a nickel electrode for an alkaline storage battery, of which active material is mainly composed of nickel hydroxide, rare earth element such as Yb, Eu, Er is contained in the nickel hydroxide in the solid solution condition. Or, furthermore, cobalt or zinc is contained in the solid solution condition. The active material desirably has the composition formula expressed with (Ni1-a Xb Coc Znd )(OH)2 . X means one or more kinds of Yb, Eu, Er, a=b+c+d, 0.02<=a<=0.20, 0<=c<0.20, 0<=d<0.20. Oxygen overvoltage of the nickel hydroxide can be raised by including the rare earth element in the nickel hydroxide in the solid solution condition. Furthermore, charging reactive electric potential in the high temperature condition can be lowered in a range, in which the discharging electric potential of the nickel electrode is not lowered, by containing the cobalt.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nickel electrode for alkaline storage batteries used in nickel-cadmium storage batteries, nickel-hydride storage batteries, nickel-zinc storage batteries and the like.

[0002]

2. Description of the Related Art Various alkaline storage batteries such as nickel-cadmium storage batteries, nickel-hydride storage batteries and nickel-zinc storage batteries using a paste type nickel electrode containing no cadmium as a positive electrode have high energy density and low pollution. For this reason, it has attracted attention, and in recent years, research and development have been actively conducted as a power source for portable devices or electric vehicles.

The paste type nickel electrode used in these alkaline storage batteries uses an electrode substrate such as a nickel fiber porous body or a foamed nickel porous body which is a porous body of an alkali resistant metal, and nickel hydroxide powder is added to the substrate. It is prepared by filling a paste-like active material with a sticky solution.

By the way, it is known that when these paste type nickel electrodes are charged at a high temperature, the charging efficiency is lowered. This is because the difference between the charge reaction potential of nickel hydroxide and the oxygen gas generation potential is originally small, so the potential difference between the nickel hydroxide charge reaction and the oxygen gas generation reaction becomes even smaller at high temperatures, and both reactions compete. Is. Therefore, conventionally, as a means for solving this phenomenon,
To the potassium hydroxide aqueous solution used as the electrolyte,
A method of adding an aqueous lithium hydroxide solution, a method of adding cobalt in a solid solution state to nickel hydroxide crystals, and the like have been proposed.

[0005]

However, the addition of lithium hydroxide to the above-mentioned electrolytic solution has the drawback of lowering the discharge voltage and the discharge capacity at low temperatures, and it provides good battery performance over a wide range of temperatures. Will not be retained. On the other hand, the solid solution addition of only cobalt to the nickel hydroxide crystal makes the charging potential of the nickel electrode a more base potential, but at the same time makes the discharge potential also a base potential, causing a decrease in battery output. There is a point. Therefore, when these means are adopted, it is necessary to take further measures against performance improvement other than charging efficiency at high temperature.

The present invention has been made in view of the above problems, and suppresses a decrease in charging efficiency at high temperatures without decreasing a discharge potential, and an alkaline storage battery excellent in charge / discharge efficiency over a wide range of temperatures. The purpose of the present invention is to provide a nickel electrode for use.

[0007]

In order to solve this problem, the nickel electrode for an alkaline storage battery of the present invention comprises nickel hydroxide, a rare earth element, or a rare earth element and cobalt, or a rare earth element and zinc, or a rare earth element. It is characterized in that cobalt and zinc are contained in a solid solution state. Further, the rare earth element is Yb, E
It is characterized in that it is at least one of u and Er, and the active material has the following composition formula. (Ni _1-a X _b Co _c Zn _d ) (OH) ₂ (wherein one or more of X = Yb, Eu, and Er, a = b
+ C + d, 0.02 ≤ a ≤ 0.20, 0 ≤ c <0.20, 0 ≤ d <0.
20)

By containing a rare earth element in a solid solution state in nickel hydroxide, the oxygen overvoltage of nickel hydroxide can be appropriately increased. That is, it is possible to suppress the decrease in charging efficiency at high temperature without decreasing the discharge potential. In addition, by containing a rare earth element and cobalt in a solid solution state, not only to increase the oxygen overvoltage of nickel hydroxide, but also to make the charge reaction potential under high temperature base in the range where the discharge potential of the nickel electrode does not become base. In addition, the conductivity of the nickel hydroxide particles can be improved, and the utilization rate of the active material can be improved. Further, by containing the rare earth element and zinc in a solid solution state, it is possible to cause strain inside the nickel hydroxide crystal,
Γ-NiOO not only improves the utilization rate of the active material
Electrode swelling due to generation of H can also be suppressed. Further, by containing the rare earth element and cobalt and zinc in a solid solution state, these effects can be obtained in combination.

Therefore, by producing a nickel electrode using these methods, it is possible to suppress a decrease in charging efficiency at high temperatures without lowering the discharge potential, and to obtain an alkali excellent in charging / discharging efficiency in a wide range of temperatures. It is possible to provide a nickel electrode for a storage battery.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments.

First, nickel hydroxide in which Yb is solid-dissolved is prepared by adding a predetermined amount of ytterbium nitrate to nickel nitrate, stirring the solution while dropping the aqueous sodium hydroxide solution, and maintaining the pH in the range of 11 to 14. The particles were precipitated, washed with water and dried to obtain a nickel hydroxide powder having the desired composition.

Further, similarly to the above, a predetermined amount of ytterbium nitrate and one or both of cobalt nitrate and zinc nitrate are added to nickel nitrate, and the aqueous sodium hydroxide solution is agitated while being dropped. The same nickel hydroxide powder was also obtained.

Further, nickel hydroxide powder prepared by a similar method to the above-mentioned nickel hydroxide powder without adding ytterbium nitrate was also obtained.

Various nickel hydroxide powders thus obtained were mixed with cobalt monoxide as a conductive auxiliary agent, and an aqueous solution in which a thickener was dissolved was added to form a paste, which was filled into a nickel fiber substrate and dried. Then, the nickel electrodes were manufactured by pressing to a predetermined thickness, and used as electrodes A to E of the present invention and comparative electrodes F to H. These were used as positive electrodes, and a known sinter-type cadmium electrode was used as the negative electrode to form a positive electrode capacity-regulated electrode group. Then, an aqueous solution of potassium hydroxide having a specific gravity of 1.28 was excessively injected as an electrolytic solution, left for 24 hours, and then charged for 15 hours at a current equivalent to 0.1 C of the theoretical capacity of the nickel electrode, and at a current equivalent to 0.2 C. Charging and discharging, which is one cycle of discharging until the potential between the electrodes reaches 1 V, was repeated 5 times to perform sufficient activation. After that, various charge / discharge tests were performed using these batteries.

The composition of the nickel electrode thus prepared is shown in Table 1.
Shown in

[0016]

[Table 1]

First, with respect to the electrodes A to B of the present invention and the comparative electrode F described above, the relationship between the high temperature charging efficiency and the Yb content is shown in FIG. The test conditions were such that the electrode was charged at a temperature of 45 ° C. for 15 hours at a current equivalent to 0.1 C of the theoretical capacity of the nickel electrode, and then discharged at a current equivalent to 0.2 C until the potential between the electrodes reached 1 V. Is. Further, the charging efficiency at 45 ° C. was expressed as a percentage with the charging efficiency at 20 ° C. being 100 (hereinafter the same). It can be seen from FIG. 1 that the charging efficiency increases as the Yb content increases. This is because the oxygen overvoltage of nickel hydroxide increases by containing Yb in a solid solution state, but the oxygen overvoltage increases as the content of Yb increases, so that the potential difference between the charging reaction and the oxygen gas generation reaction is increased. It is considered that the battery can be made larger and the charging efficiency can be improved.

Next, with respect to the electrodes A and C of the present invention and the comparative electrode G described above, the relationship between the high temperature charging efficiency when Yb or Co is contained and the Co content is shown in FIG. The test conditions were the same as in the evaluation in FIG. 1, at a temperature of 45 ° C., after charging for 15 hours with a current equivalent to 0.1 C of the theoretical capacity of the nickel electrode, a potential equivalent between the electrodes was changed to 0.2 C at a current equivalent to 0.2 C. It was discharged up to 1V.

As is apparent from FIG. 2, when Co is contained, the comparison electrode G to which Yb is not added has a good charging efficiency at a relatively high temperature. The batteries A and C have better charging efficiency. The battery C of the present invention containing Co at the same time as Yb is
The charging efficiency is further improved as compared with the battery A of the present invention to which only is added. It is considered that this is because Co has the effect of making the charge reaction potential under high temperature more base, so that the synergistic effect with Yb can increase the potential difference between the charge reaction under high temperature and the oxygen gas generation reaction. . Further, since Co takes the form of a higher-order oxide, the conductivity inside the nickel hydroxide particles can be improved, and the utilization rate of the active material can be expected to improve. However, when a large amount of Co is added, the discharge reaction potential also becomes base, so it is necessary to limit the addition amount to an appropriate range.

FIG. 3 shows the relationship between the Zn content and the high temperature charging efficiency when the electrodes A, D and E of the present invention and the comparative electrode H described above contain Yb or Zn. The test conditions were the same as the evaluations in FIGS. 1 and 2, after charging for 15 hours at a current equivalent to 0.1 C of the theoretical capacity of the nickel electrode at a temperature of 45 ° C., and then between the electrodes at a current equivalent to 0.2 C. It was discharged until the potential reached 1V. As is apparent from FIG. 3, the electrodes D and Z of the present invention containing Zn and Yb at the same time.
The charging efficiency of the electrode E of the present invention containing n, Co and Yb at the same time is improved. In addition, even when Zn is contained, Y
In the comparative electrode H to which b is not added, the charging efficiency is rather lowered. Furthermore, the electrode D of the present invention containing Zn and Yb at the same time has a higher charging efficiency than the electrode A of the present invention containing only Yb. It is considered that this is because Zn has the effect of making the oxygen generation potential noble, so that the potential difference between the nickel hydroxide charge reaction and the oxygen gas generation reaction can be increased. Further, since Zn has an ionic radius different from that of Ni, it is possible to cause strain inside the crystal of nickel hydroxide, which not only improves the utilization rate of the active material, but also
The effect of suppressing the electrode swelling due to the production of γ-NiOOH can be expected. The effect of these Zn is that when Zn alone is added, the high temperature charging efficiency is lower than that when only Yb is added, but simultaneous addition with Yb or simultaneous addition with Co and Yb is observed. However, the synergistic effect with the addition effect of Yb and Co described above can be favorably obtained.

From the above, the electrodes A to E of the present invention suppress the deterioration of the charging efficiency at high temperature without lowering the discharge potential, as compared with the comparative batteries F to H, and have a wide temperature range. It can be seen that this is a nickel electrode for alkaline storage batteries, which has excellent charge / discharge efficiency.

In the present embodiment, Yb was contained in the nickel hydroxide powder in a solid solution state, but E which is a rare earth element was used.
Even if u or Er is contained, the same effect can be obtained. Further, when Eu or Er and Co, Eu or Er and Zn, or Eu or Er and Zn, Co are contained at the same time, or when Yb, Eu or Er is added at the same time, further, Yb, Eu or Er and Co are added. , Or Yb, Eu or Er and Zn, or Yb, Eu or Er and Zn, Co
The same effect can be obtained when both are simultaneously contained. Furthermore, it is also effective to contain other rare earth elements.

[0023]

INDUSTRIAL APPLICABILITY As described above, the present invention can provide a nickel electrode for an alkaline storage battery having excellent charge / discharge efficiency over a wide range of temperatures and having stable capacity characteristics, and its industrial value is great.

[Brief description of the drawings]

FIG. 1 is a high temperature charging efficiency and Y in the present invention and a comparative example.
It is a figure which shows the relationship with b content.

FIG. 2 shows Yb or Co in the present invention and comparative examples.
It is a figure which shows the relationship between the high temperature charging efficiency at the time of containing, and Co content.

FIG. 3 shows Yb or Zn in the present invention and comparative examples.
It is a figure which shows the relationship between the high temperature charging efficiency at the time of containing, and Zn content.

Front page continued (72) Yuichi Matsumura, 6-6 Josaimachi, Takatsuki-shi, Osaka Prefecture, Yuasa Corporation (72) Masahiko Oshiya, 6-6, Josaimachi, Takatsuki, Osaka Prefecture, Yuasa Corporation

Claims (6)

[Claims] 1. A nickel electrode for an alkaline storage battery, which comprises nickel hydroxide as a main component of an active material, and a rare earth element is contained in the nickel hydroxide in a solid solution state. 2. A nickel electrode for an alkaline storage battery, comprising nickel hydroxide as a main component of an active material, wherein the nickel hydroxide contains a rare earth element and cobalt in a solid solution state. . 3. A nickel electrode for an alkaline storage battery, which comprises nickel hydroxide as a main component of an active material, wherein the nickel hydroxide contains a rare earth element and zinc in a solid solution state. . 4. A nickel electrode for an alkaline storage battery, which contains nickel hydroxide as a main component of an active material, wherein the nickel hydroxide contains a rare earth element and cobalt and zinc in a solid solution state. Nickel electrode. 5. The nickel electrode for an alkaline storage battery according to claim 1, wherein the rare earth element is at least one of Yb, Eu and Er. 6. The nickel electrode for an alkaline storage battery according to claim 1, wherein the active material has a composition formula shown below. (Ni _1-a X _b Co _c Zn _d ) (OH) ₂ (wherein one or more of X = Yb, Eu, and Er, a = b
+ C + d, 0.02 ≤ a ≤ 0.20, 0 ≤ c <0.20, 0 ≤ d <0.
20)